In the automobile field, a number of electrical components or parts have been recently used for various purposes, in order to improve fuel efficiency, comfortable ride, safety, and others. Those purposes include many things, for example, various electronic control equipments or sensors of combustion or running represented by ECU (Electrical Control Unit), interior or exterior lighting associated equipments, air-conditioning equipments, and motor-driven equipments (such as windshield wipers or power windows). Along with an increase of electrical components, the number of wires in an automobile also increases for the purpose of transmission of an electric power or a controlling signal to activate those electrical components. Such a material employed in wiring (e.g., a covering material for wire) requires a high durability or a high flame retardancy.
So far a polyvinyl chloride resin has been used as a material excellent in durability or flame retardancy. In the light of flame retardancy, it has been known that a halogen-containing flame retardant can impart a high-level flame retardancy to a resin or the like. However, from the viewpoint of the burden on the environment, a halogen-free material, for example, a material containing a flame-retardant polyolefin, a flame-retardant polyester elastomer, or the like as a main or base component (particularly, a material that does not contain any halogen-containing flame retardant) is attracting attention.
As such a material, for example, Japanese Patent Application Laid-Open No. 53007/1997 (JP-9-53007A, Claims 1 and 2) discloses a flame-retardant resin composition that comprises (A) a polyester block copolymer and (C) a phosphorus compound and/or a triazine compound and if necessary (B) a polyalkylene terephthalate resin in a proportion of 5 to 150 parts by weight of the compound (C) relative to 100 parts by weight of the total amount of the polyester block copolymer (A) and the polyalkylene terephthalate resin (B). In the resin composition, the polyester block copolymer (A) comprises a polybutylene terephthalate as a hard segment and a polyester as a soft segment, and the polyester comprises an aromatic dicarboxylic acid and a long-chain diol having a carbon number of 5 to 12 as main units. In addition, the document discloses an electric wire that has an electric conductor covered the outside with the resin composition as a covering material. Moreover, Japanese Patent Application Laid-Open No. 30204/2002 (JP-2002-30204A, Claims 1 and 12) discloses that the following flame-retardant polyester elastomer resin composition is suitable for covering of an electric wire or an optical fiber: the resin composition comprises 100 parts by weight of (A) a polyether ester block copolymer comprising (a) a high-melting point crystalline polymer segment containing a crystalline aromatic polyester unit and (b) a low-melting point polymer segment containing an aliphatic polyether unit as main units, 1 to 50 parts by weight of (B) a phosphorus-containing compound, and 0.01 to 10 parts by weight of (C) a monocarbodiimide compound and/or (D) a polycarbodiimide compound.
However, such resin compositions have a low hydrolysis resistance. In addition, those compositions require a large amount of a flame retardant in order to improve the flame retardancy, so that the properties of the resin are significantly deteriorated. Moreover, the use of a phosphate ester compound as the phosphorus compound has some problems such as deterioration in external appearance and electric properties caused by bleeding out (blooming) derived from the phosphate ester compound (e.g., deterioration in volume resistance) and deterioration in heat resistance. Therefore, a material having properties necessary for a wide range of uses in the automobile field (for example, toughness, heat resistance, hydrolysis resistance, and burning resistance) has been required.
Moreover, Japanese Patent Application Laid-Open No. 358837/2002 (JP-2002-358837A, Claims 1 and 4 to 6) discloses a flat cable having an insulating covering (or coating) that comprises the following polyester resin composition: the resin composition comprises 100 parts by weight of (A) a thermoplastic aromatic polyester, 10 to 120 parts by weight of (B) a polyester block copolymer containing a polytetramethylene terephthalate as a hard segment and a polyester containing an aromatic dicarboxylic acid and a long-chain diol having a carbon number of 5 to 12 as a soft segment, and 1 to 50 parts by weight of (C) an olefin-acrylate copolymer modified with a glycidyl compound. This document also discloses that the resin composition may contain a phosphorus-containing flame retardant or a polycarbodiimide compound. However, such a resin composition lacks abrasion resistance or enough flame retardancy.
On the other hand, Japanese Patent Application Laid-Open No. 73720/1996 (JP-8-73720A, Claim 1) discloses a method for using a specific calcium or aluminum phosphinate for a polyester resin. While the salt can impart a flame retardancy to the resin, such a resin composition is insufficient in flexibility or toughness. Therefore, the resin composition is not suitable for a covering (or a coating) of an electric wire.